iExplorer currently can only export contacts directly to the Mac OS X Contacts app on a Mac. If you need the CSV format, you have a couple options. If you have access to a Windows computer or have Boot Camp setup, you could use the Windows version since it exports files directly to a folder as vCard or CSV files.
Or, from the Mac Contacts app, you could export them as vCard file(s) to a folder and then use another program to convert the vCard(s) into a single CSV file. The Contacts app’s File menu > Export… has a vCard option. Just be sure to select them all first since it exports the selected contacts to vCard. You can select one and press Command-A to select them all.
We plan to add the ability to export contacts directly from the Mac version of iExplorer as vCard and CSV like the Windows version does, but I don’t have an ETA on when it will be added. Right now, you can only export directly to the Contacts app.